At the Chamber of Sins Cruel on my Marauder Facebreaker. Picked up the Blood Magic support gem for Infernal Blow, and combined with Life on Hit and Additional Melee Damage the ability is pretty powerful. Able to handle areas that are a level or two higher than I am as long as I play somewhat cautiously. Have enough life and life regen that I gain back what spend on IB before I can swing again, so the health cost is almost nonexistent.
Here's where I'm at now. Aiming to pick up the elemental resistance and life/life regen nodes near Vaal Pact.